


Staking a Claim

by halcyon1993



Series: The Kinky Adventures of a Wolf and His Boy [7]
Category: Teen Wolf (TV)
Genre: Adopted Stiles Stilinski, Anal Fingering, Anal Sex, Body Worship, Bottom Stiles Stilinski, Come Marking, Daddy Kink, Dark Derek Hale, Dubious Consent, Father/Son Incest, Impregnation, M/M, Mental Health Issues, Non-Consensual Drug Use, Older Derek Hale, Oral Sex, Plot What Plot/Porn Without Plot, Possessive Behavior, Pseudo-Incest, Rimming, Size Difference, Somnophilia, Top Derek Hale
Language: English
Status: Completed
Published: 2018-02-22
Updated: 2018-02-22
Packaged: 2019-03-22 16:41:43
Rating: Explicit
Warnings: Rape/Non-Con, Underage
Chapters: 1
Words: 8,134
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/13768248
Author URL: https://archiveofourown.org/users/halcyon1993/pseuds/halcyon1993
Summary: Derek loves his adopted son, Stiles. Maybe too much. He tries to resist for a long time, but when Stiles gets older and starts showing an interest in his peers, Derek worries that they will take his son away from him. He'll just have to get there first.





	Staking a Claim

**Author's Note:**

  * For [clavius](https://archiveofourown.org/users/clavius/gifts).



> Don't judge me for the depravity I have written...
> 
> I do not condone anything like this happening in real life. This is purely make-believe. By the time the actual smut happens in this PWP, Stiles is 14 years old and Derek is 39. If this offends/bothers/disgusts you, I suggest you don't read it.

Derek Hale had always wanted kids. Even when he was one himself, he knew he wanted to have a big family when he grew up, a husband or wife with whom he could raise several children. This need only got stronger when he was in his late teens and his parents and siblings died in a house fire, leaving him alone with a gaping void in his chest that he proceeded to try to fill. But for over a decade, it looked like his dreams would never come true.

Everyone Derek tried to have a relationship with wanted different things than he did:

They were with him just for his looks.

They didn't want something serious or long-term.

They didn't want kids.

As Derek was approaching his thirtieth birthday, he contemplated just giving up on his dream altogether. Fate seemed set on denying it to him, so what was the point of continuing to hope? It only ended in depression and hurt feelings. It was getting difficult to convince himself to leave the house for anything other than work, and Derek did it less and less often. He stopped talking to the few friends he had, and eventually all but one stopped trying to talk to him.

Of course, just when he was about to commit himself to a life of being alone, that's when Stiles came along. He was a toddler when Derek first met him at an orphanage that the only person he had managed to stay friends with, Jordan Parrish, had dragged him to. Parrish had needed to see things firsthand for an article he was writing for their local newspaper, but he didn't want to go alone. Derek reluctantly agreed to help.

While Parrish was off conducting an interview, Derek was sitting in an empty room, minding his own business, when the door opened and a tiny face peered in. Derek was immediately enraptured by the boy's huge Bambi eyes and cute little nose. The boy had stared at him for a few seconds and then retreated, but Derek needed to know more. When Parrish had acquired all the information he needed for their article, Derek stayed behind at the orphanage and asked one of the people who worked there about the boy he'd seen. He was told his name and a bit about him.

The boy was called Mieczysław Stilinski, but everyone just called him Stiles because his real name was too difficult for most people to pronounce, especially the other kids. His parents were murdered in a break-in at their house, a tragic backstory that made Derek feel a kinship to him. They'd both lost their families in horrific events, and it seemed perfect, like the fates were finally giving him someone to make up for starving him of companionship for so long.

Because of his past, Stiles was shy and afraid of meeting new people. He didn't have any friends at the orphanage and mostly just played by himself, something that had made Derek sad to learn, but also more determined. Maybe they could be what each other needed. He looked into adoption and visited Stiles whenever he could, seeking to build trust between them.

The first visit went about as well as he had expected, with Stiles keeping his distance and barely saying a word. But Derek kept at it, and he'd never forget the first time Stiles asked him if he wanted to play with him using some toy cars that had recently been donated to the orphanage. Derek had eagerly agreed, and from then on Stiles got progressively more talkative, eventually reaching the point where he would hardly stop to breathe. Derek just listened and smiled, finding it adorable. He didn't mind, because he himself wasn't much of a talker and it was nice to have the silence filled. It was impossible to even think about being annoyed with the little boy anyway.

Things continued this way until Derek's application for adoption finally went through and he was approved. By then, he had already begun thinking of Stiles as his son, and when he told Stiles the good news, the boy burst into tears and hugged his legs so tightly that, for a long time, Derek couldn't pry him off for anything.

For the first few months, everything went smoothly. Stiles still called Derek by his first name, but things were new back then and Derek was patient. He moved his new son into his two-storey house on the outskirts of Beacon Hills and enrolled him in the local preschool, where, with Derek bolstering his confidence, he quickly made a friend in the form of the asthmatic Scott McCall. The pair were inseparable, and Derek saw a lot of Scott and his mother, Melissa. Sometimes too much.

There was a tiny part of Derek that didn't like having so much of Stiles' time occupied by the McCalls, didn't like Stiles' attention not being fixed on him. It was just his need to not be alone rearing its ugly head again, he knew. It was selfish, so he didn't let it affect his son's friendship in any way.

Then, about six months after Stiles came to live with him, things took an unexpected turn. Derek was kneeling next to the bathtub, helping Stiles get washed and ready for bed, when the boy called him 'daddy' for the first time. It was such a shock that Derek didn't immediately register his body's reaction to the word, how the crotch of his jeans got tighter. When he did, he was so deeply ashamed that he also nearly missed what his lack of response did to Stiles. The boy had looked terrified, interpreting Derek's silence as him not liking being called that. When he finally managed to push through his shock, Derek plastered a reassuring smile on his face, ruffled his son's hair and Stiles had perked right back up again, all traces of fear forgotten.

Derek hoped it was just a one-time thing, but he quickly found out that that wasn't the case. From that evening on, every time Stiles called him 'daddy', Derek would feel the heat of arousal in his gut and he would have to work hard to make sure no one figured it out.

He told himself that he just had a daddy kink he had never discovered before, that the fact that it was _Stiles_ calling him 'daddy' had nothing to do with it. He went out a few times, whenever Stiles was having a sleepover at the McCalls', and tried to figure some things out. Looking the way he did, it wasn't difficult to find a younger guy to fool around with, but he couldn't get into it—not even when he found a twink who had no problem indulging him in his suspected daddy kink. The word did nothing for Derek when it came from the lips of some stranger.

It was Stiles who did it. Derek was disgusted with himself for a long time, but his reaction to his son saying that word never went away, no matter what he did.

Nine years after adopting Stiles, Derek's control was finally beginning to wane. Even at thirteen, Stiles still called him 'daddy' instead of switching to 'dad', probably because Derek did everything he could to encourage the boy to stay young and innocent for as long as possible. Each time Derek heard that word, his resolve crumbled a bit more. It didn't help that his son had been found to be a carrier during one of his checkups with the paediatrician, meaning he was capable of becoming pregnant. _Derek_ could get him pregnant.

Derek barely restrained himself from doing something unspeakable whenever Stiles rambled on about how beautiful one of the girls in his year was, a redhead named Lydia Martin, or about how amazing one of the boys was, a Hawaiian named Danny Mahealani. Derek got terribly jealous every time, and while he knew he shouldn't feel that way, he couldn't help it. Maybe something deep inside him broke when he lost his family, or maybe he was always this fucked up in the head and had just never realised it before, but now that he had Stiles, Derek was honestly scared of the lengths he thought he might go to in order to keep him.

His jealousy got so bad that Derek knew he wouldn't be able to hold out much longer—and he was right.

On the day of Stiles' fourteenth birthday party, Derek was in the middle of cutting even slices of cake for all of the guests when he overheard a conversation between Stiles and Scott. The latter was boasting about some girl called Allison letting him cop a feel behind the school building. Stiles was envious and wondered aloud when he would get to do something like that, and the thought of his baby boy touching someone else that way—the thought of someone else touching Stiles that way—was too much for Derek to handle. He couldn't fight it. His resolved crumbled completely, and he knew he had to claim him that very night.

Stiles was _his_ , and no one was going to take him away.

Now, Derek is cleaning up in the kitchen after all the guests have gone home. He faces the sink and washes up plates and cutlery when he hears footsteps behind him. Glancing over his shoulder, he sees Stiles enter the room dressed in a pair of thin black pyjama bottoms and a red hoodie unzipped all the way, showing off a sliver of his lanky pale torso. It's an enticing sight, but Derek doesn't let it show how much it affects him.

"What's this?" Stiles asks, pointing to the slice of cake sitting out on the kitchen table. Next to it is a glass of warm milk.

"Yours," Derek replies, returning his eyes to the sink before he gives in to the urge to rip Stiles' clothes off of him then and there.

"What? I thought I was only allowed one."

"I changed my mind. It's your birthday after all, so just this once won't hurt."

There are a few moments of silence and then Derek is spun around, the rubber gloves on his hands spraying soapy water everywhere, and Stiles hugs him, the top of his head just missing Derek's chin.

"Thank you!" the teenager says into his chest. "You're the best daddy ever!"

"You're welcome," Derek chokes out.

He is grateful when Stiles pulls away a second later, because any longer and the boy would have surely felt his traitorous cock getting hard in his jeans. The two will be introduced very soon, but Derek doesn't want to risk scaring off his son before they can really begin. He turns quickly back to the sink to finish washing up the dishes as an unsuspecting Stiles takes his cake and milk into the living room to wind down with some television.

Patience, Derek tells himself. Another hour, if that. He can make it. He has held out for this long, so one more measly hour will be easy as pie.

He washes the last few dishes in the sink and dries his hands on a dishtowel that he throws carelessly on the side when he is done with it. He follows the sounds of talking and peeks in on Stiles in the living room. His spying goes unobserved by the boy, whose attention is focused half on the TV screen and half on the cake he is eating with his hands.

Derek isn't surprised to see frosting around Stiles' mouth. His son has never been the neatest eater, and he wonders if that will ever change. It reminds him of the hundreds of times after he had first adopted Stiles, when they were eating together and he'd always had to have a napkin handy for when they finished and Stiles' face was invariably a mess. Something about the teenager still eating sloppily feels so innocent, like his son is staying young and dependent on him and always will. It's a wonderful thought, that Stiles will never leave him, and it helps to calm the possessiveness that roars through his veins.

Derek stays in the doorway for quite a while, just watching his son. He is far more beautiful than he has any right to be. Honestly, how was Derek supposed to keep resisting? It's a miracle he lasted as long as he did, really.

He keeps leaning against the doorjamb until Stiles finishes eating and moves on to his milk, which has Derek holding his breath. He waits for Stiles to notice that something is different about the drink, to make a confused or disgusted face and stop drinking it, but he doesn't. Only when the last drop has gone down Stiles' throat and several minutes have passed does Derek breathe again and make his presence known. By then, Stiles' eyes are drooping and Derek knows he has to get him to bed before the sedatives he had mixed into the milk really kick in. He feels bad for doing this to his son, but he is sure that Stiles will understand once it's all over.

"Hey, baby, you look tired," Derek comments, coming to stand in front of him.

"Yeah…" Stiles groans, pouting cutely. "I guess today wore me out more than I thought."

"Okay, let's get you to bed, huh?"

Derek switches off the television and scoops Stiles up into his arms. The boy doesn't protest at all, just tucks his face into his neck, nearly causing Derek to stumble. Maybe his son is already too sleepy to complain, but Derek chooses to believe that Stiles doesn't mind being carried to bed like a small child.

He manages Stiles' weight with no problem. He has always prided himself of staying in shape, even now that he is thirty-nine years old, and Stiles has always been on the skinny side anyway. The muscles of Derek's arms aren't aching at all by the time he has kicked open Stiles' bedroom door and carried him over to the double bed. He is gentle as he lays his baby boy down atop the mattress and cleans off his face with a hand towel he gets from the bathroom down the hall.

When that is done, Stiles can barely keep his eyes open, so Derek pulls the covers up from where they have been flung to the foot of the bed since that morning. He tucks Stiles in and brushes back the hair from his forehead, a tender smile on his lips. He usually enjoys taking care of his son, and in that way, tonight is no different. But in another way, it is.

It's an act he is putting on so that Stiles doesn't get suspicious too early, because Derek knows that as soon as his son succumbs to the sedatives, it will be time for him to make it known to Stiles that he is _his_ and will never be anyone else's. He strokes his fingers through Stiles' hair and watches as his eyes flutter and he turns slightly toward him, seeking more of his touch.

"Goodnight, baby," Derek whispers, his hand drifting from Stiles' hair to stroke across his cheek.

"Mmm…'night," the boy mumbles, the words slurred.

It only takes a few more moments for Stiles to go under, and when he does, Derek retracts his hand, steps away from the bed and leaves the room to get ready. He pads back to the bathroom, drops the damp hand towel in the laundry hamper and stares at himself in the mirror above the sink.

This is his last chance to back out. It's not too late yet. He can go to his own bed right now, go to sleep, and they will both wake up tomorrow as normal. Stiles will be none the wiser. It's not right to do this, especially not to knock up his fourteen-year-old son like he plans on doing. His young body would struggle to accommodate a pregnancy.

Derek _should_ just go to his own bed. The tiny part of his brain that is still thinking rationally knows this, but Derek doesn't— _can't_ —listen to it. He reminds himself of what Stiles had said to Scott a couple of hours ago and how he can't allow someone else to get their hands on his son. Stiles belongs to _him_. No one else will treat him how he deserves, so Derek must be doing the right thing.

He tears his eyes away from his own reflection and pops the button of his jeans. He kicks them off, not caring where they land, and does the same thing with his boxer-briefs and henley. Totally naked, Derek relieves himself in the toilet before exiting the bathroom and entering the master bedroom for some supplies. He raids the top drawer of his nightstand and pulls out the half-used tube of lubricant he keeps there for when he jerks off late at night—usually to thoughts of Stiles moaning beneath him. He stares down at the lube and realises that he can't count the times he has done that. Maybe thousands by this point. Maybe this was always an inevitability.

Either way, it's happening, and Derek carries the lube with him on his way back to Stiles' bedroom.

The boy is right where he'd left him, half turned on his side to face the side of the bed where Derek had been stood. He seems even younger than fourteen somehow, is the picture of innocence, and Derek is about to take that innocence for himself before someone else can.

He approaches the bed and slowly pulls down the sheets with his free hand. Once they are clear of Stiles' body, he rips them the rest of the way off the bed and throws them into the corner of the room. Derek doesn't need them for what he has planned. He kneels next to his son on the mattress, turns him fully onto his back and pauses briefly to gauge the boy's reaction, but there isn't one. The drugs are doing their job, so Derek feels a bit braver and pulls open the sides of Stiles' hoodie to reveal the entirety of his torso.

He doesn't stop to look just yet, not wanting to spoil the full effect. Instead, he concentrates on working the long sleeves down Stiles' arms and then easing the hoodie out from beneath him. It joins the bedsheet in the corner and, now that Stiles is topless, Derek allows himself to look.

The boy is a thing of beauty, just like Derek always knew he was. He can't resist getting his hands on that body. He manoeuvres himself between Stiles' legs and runs his hands over every inch of bare, pale skin he can touch. It's so silky-smooth, all apart from the fine hairs that grow in a trail down from Stiles' bellybutton to the waistband of his pyjama bottoms.

Derek looks down at himself and thinks their bodies contrast well with each other. Where Stiles is nearly hairless, small and delicate, with barely any muscle on him, Derek is hairy and strong, with muscles that nearly everyone lusts after when he walks down the street. He hopes that Stiles' body will always be as smooth as it is now.

He cups his son's barely developed chest and plays with his small, dusky nipples, pinching and rolling them between his index fingers and thumbs. Stiles doesn't so much as twitch, so Derek continues his ministrations until his son's nipples are red, swollen and raw-looking. He leans over him and sucks on them, biting them softly between his teeth and then soothing them again with small swipes of his tongue.

Stiles' skin tastes so good, better than Derek had ever allowed himself to imagine. He has to have more, has to taste the boy everywhere.

He draws away, curls his fingers around the waistband of Stiles' pyjama bottoms and prepares himself for what he is about to see. When he believes himself ready, he gradually pulls the garment down and off and then, starting with his feet, he drinks in the sight of his baby boy bared to him completely.

Stiles' feet are large for his size, nearly the same size as Derek's, which he knows from the last time they went shoe shopping together. Feet have never done anything for him before, but because they belong to his son, Derek finds them hot.

Next are Stiles' legs. They are just as skinny and pale as the rest of him and are dusted with brown hairs finer than those on Derek's legs. The man picks the right one up and runs his mouth up the calf, enjoying the way the hairs tickle his lips. He keeps going up the boy's inner thigh, where there is basically nothing but soft skin, and then he goes further still, until he reaches the crease where Stiles' leg meets his groin.

Derek nuzzles into the boy's hip before moving to the right so that his nose ends up right in the small thatch of curls that surrounds the base of Stiles' flaccid cock. He lingers there for a long time, his eyes closed as he just breathes. The scent of his son's sex has his own cock throbbing between his hairy thighs, rock-hard and leaking with impatience, but he doesn't move to touch himself. It's not quite time for that yet.

Because of the sedatives Derek gave him, Stiles didn't get a chance to wash himself before bed and so his scent is musky from a day filled with excitement. Derek can't wait to experience how pungent it gets when they are both finished, when Stiles is covered in their combined come and sweat. He just knows it's going to be fucking amazing.

When he finally has his fill, Derek removes his nose from Stiles' pubes but keeps his face close to the boy's crotch. He thinks that Stiles' little cock is cute where it rests over his hairless balls. It's circumcised, yet another difference between them, and Derek wouldn't change a thing about it. He cradles it in his palm and laps at the slit a couple of times before taking it wholly in his mouth.

It fits easily. Derek sucks him while fondling Stiles' balls and is pleased when, after a minute, he feels his baby's body begin to respond to the stimulation. The cock in his mouth gradually gets bigger and firmer, until it's fully hard and just touches the back of Derek's throat when he takes it all the way, pubic hair scratching at his barely stretched lips.

Excited by this new development, Derek pulls off and shuffles forward on his knees so that he can line their cocks up, the undersides touching from root to tip and his heavy balls sitting atop Stiles'. Stiles is still growing, but even now Derek can tell that he will always dwarf his son. At eight inches himself, he is thicker and approximately two and a half inches longer. He wraps his hand around them both and uses his own pre-come to slick the way, making it easier to stroke over Stiles' cut head.

Once again, the contrasts makes for a marvellous sight, something Derek just can't get over. There is the fact that he is hairier than his son there, too, his pubic hair dark and untamed, whereas Stiles' is a bit lighter, finer and sparser. There is the size difference between them, of course, and then there is the image of his son's perpetually bare cock head next to Derek's covered one, his foreskin hiding the head of his own cock on every upstroke and then pulling back to reveal it every time Derek slides his hand down to the base, bringing the excess skin with it.

It's hypnotic in a way, and he muses that he could probably spend a long time just watching their cocks in his hand without getting bored. He indulges in just that for a few moments, but then he moves on, knowing he has to hurry up if he doesn't want the sedatives to wear off too early.

Derek releases Stiles' cock and moves further up his body so that he straddles his chest without putting any weight on it. His low balls just graze Stiles' collarbones as he positions the tip of his cock over the boy's lips. Holding himself at the base, fingers tangling in his pubes, he wipes his cock head over Stiles' closed mouth, back and forth, back and forth, coating it with his pre-come.

He doesn't stop until those perfect cock-sucking lips are slick and shiny, glistening in the warm glow from the overhead light. This is something he has fantasised about for years, his cock in front of his son's pretty face. And it's about to get even better.

Releasing himself, with both hands Derek picks Stiles' head up off of the pillows and then cups the back of it with just his left, freeing his right. He repeats what he had just done with his cock with his right index finger, skating it across his baby's lips before pressing it down against the bottom one to part them. He opens Stiles' mouth so that his jaw is slack and it's shaped like a perfect O.

Derek's cock throbs again as he moves his hips forward and slips the tip through this O, keeping Stiles' head steady with both hands again. He thrusts shallowly a few times, enjoying the heat and warmth of the inside of Stiles' mouth before daring to venture deeper. He feels the tip of his cock hit the back of the teenager's throat when he is only halfway inside, and he considers easing off. But only briefly. The temptation of his son's throat constricting around him as he struggles not to choke is too much to ignore, getting Derek moving as if his body is on autopilot.

The position isn't the best, bending his cock downward as he forces himself where he wants, but it will do. It still feels amazing, especially when he manages to get the entirety of his cock head into Stiles' throat before the boy convulses. He enjoys the sensation before pulling back and allowing Stiles' body to take a few breaths. Once he has, Derek repeats the whole process, over and over again until he can fit nearly the entirety of himself in Stiles' mouth. He is shy just an inch, but he knows he'll have the rest of their lives to train his son to take him all the way.

Derek continues to thrust into Stiles' mouth and throat, enjoying each convulsion every time he is almost all the way in. He slowly speeds up but never attempts to fit that one last inch inside. His weighty balls swinging between his thighs, occasionally glancing off of Stiles' chin, he keeps going until he feels the familiar heat in his gut that tells him he is close to coming.

Just before he reaches his climax, Derek withdraws all the way from Stiles' mouth, lets the boy's head fall back against the pillows and strips his cock quickly to bring himself the rest of the way there. It takes just a few seconds, and then he is spurting hot and sticky all over his son's face. He nearly tips his head back and closes his eyes in bliss, but he manages to push through his natural reaction to this particular pleasure and instead stares down at the mess he is making.

The visual seems to prolong Derek's orgasm, but eventually it ends and he breathes heavily as he comes down and admires his handiwork. Stiles' face is dripping, coated in his daddy's huge load. It's up in his hair, a couple of pulses across his forehead and over his closed eyes. There are viscous stripes right across the bridge of his nose, over his fair cheeks, and then several more over his lips. They are still parted from Derek fucking his mouth, so some of the seed gets inside, drips down onto his tongue.

Derek almost wishes that his son was awake so that he could witness him enjoying this special treat, but, again, he tells himself there is always later.

Derek thinks that covering his son's face in his come is almost like a claiming act, like he is marking him as his property. Stiles _is_ his property, and even though the act is already done, this thought has his possessiveness flaring up again and he has to go one step further.

He shifts backward to straddle Stiles' waist instead of his chest and then, using the index and middle fingers of his right hand, he scoops up a glob of come from Stiles' face and transfers it to his chest. It's almost like he is finger-painting. His come is the paint and Stiles' body is the canvas; the most gorgeous canvas in the world. He does this several times, taking the come from his son's face and putting it on his chest instead, until he has enough to rub it into his skin like massage oil.

When the last trace of it is gone, friction making their skin dry again, Derek puts his nose against the centre of Stiles' chest and inhales. He grins, satisfied, when he finds that he can clearly smell himself all over his baby.

With this success, Derek switches back to the come still on Stiles face and does the same thing there, moving it around until it resembles a sick face mask.

When this, too, is dry, Derek knows it's time to start preparations for the main event. If his admittedly shoddy knowledge of the sedative he has used is true, then Stiles should wake up within the next half hour or so, so Derek doesn't have much time to spare.

Keeping this in mind, he moves wholly off of his son and pulls him down the mattress until his head comes off of the pillows. He turns Stiles over, hikes his hips up and holds them in the air while he grabs the pillows to shove beneath them. When they are in place, Derek lets Stiles go and is pleased when his hips stay up at just the right height. Wanting to get the full picture, he grabs the lube that has been lying unused this whole time, knees Stiles' legs apart and positions himself between them.

Stiles' ass is hairless, entrancing globes that invite all manner of depravity. Derek intends to deliver that. He fits his hands over that delectable ass and squeezes each cheek, testing the firmness of their musculature. There _are_ muscles there, but since Stiles doesn't work out apart from playing the occasional sport, there is also some give, the perfect amount to make them jiggle.

Derek just has to mark these, too, and so—his trust still placed in the drugs—he brings his hands down hard on Stiles' ass, one cheek after the other. He waits a second to watch for a reaction, a twitch, from Stiles, but there is nothing. Empowered to do as he pleases, Derek spanks Stiles' ass relentlessly, showing no sign of stopping until both cheeks sport a flaming-red handprint, proclaiming them as his. There isn't much point in doing this, Derek is aware, as no one but him will ever see his baby boy's bare ass, but, even so, to see his handprints fills him with savage pride.

When he is happy with the results of the impromptu spanking, Derek smooths his palms over the flaming globes of flesh to soothe them and then parts them, giving himself the first glimpse he has ever had of Stiles' little asshole.

It clenches instinctively as it is exposed to the cooler air of the bedroom, a reaction Derek wants to witness again. Momentarily letting go of Stiles' ass cheeks, he slides himself down the bed so that his shins and feet hang off of the end and he can lie somewhat comfortably on his front. Then he grabs his son's ass again, puckers his lips and blows gently on the most intimate part of Stiles' body. He does this several times, just so he can enjoy the mesmerising sight of Stiles' virgin asshole clenching and relaxing almost rhythmically.

Eventually, when he has had his fill, Derek stops blowing air and moves his face closer to rub it up and down the crack of the teenager's ass, getting the musky scent of it all over himself. It's divine, and it's all the incentive Derek needs to bring his tongue into play. He swirls it around the furled muscle to taste it, too, and wonders how it is that every part of his son is exactly what he wants. What he needs. Stiles really was made just for him, his soulmate, and even though it was innocent then, Derek knew it from the very moment he laid eyes on him.

And now that he has accepted it, accepted that no one else would approve and that he doesn't care, he revels in it.

Derek works his tongue over Stiles' asshole with more enthusiasm. He points it and wiggles it right over the opening, impatiently trying to get inside, to taste him there as well. It takes longer than Derek would like, but then he is in and his tongue is gripped tightly by burning heat. God, he can't wait any longer. If it's like this for his tongue, what will Stiles' ass feel like around his cock?

Derek never lost his arousal completely, his erection softening to a half-hard state between his thighs. But now, as he ruts against the mattress and eats his son out, his blood surges south and his cock reaches full hardness again, ready to be sheathed to the hilt in place of his tongue, to sink home.

Derek withdraws from Stiles' hole, gives it one last lick and then pops the cap on the lube. He slicks his fingers, allows the lube to warm up a bit and then positions his index finger against his son's entrance. He circles it around the muscle to slick it up and then slowly sinks it in, biting roughly into his bottom lip to hold in the moan that wants to slip out.

He thrusts his finger in and out a few times before easing another in beside it. It feels even tighter now, like his massive cock will never fit in a million years, but Derek knows he just has to be patient, has to stretch Stiles' hole so that it _can_ take him.

Watching constantly for any sign of his son is waking up, Derek scissors his fingers apart and twists them around, making more and more room for himself. When he is able to fit a third finger inside, and then his pinky, he knows Stiles is ready.

With the last one, he spotted his baby's hands twitching where they lie palms-up on either side of his hips, so he doesn't have much longer. He doesn't want Stiles to wake up until he is already inside of him, but he wants to do this face-to-face. It will be more intimate that way, and he knows that Stiles being able to see his face will make it easier for him to reassure the boy that what is happening is meant to be.

Derek wipes his fingers off on the bedspread and turns Stiles onto his back again. The boy makes a noise, a quiet whine of confusion like he is wordlessly asking why he is being disturbed, but this noise is ignored. Derek wraps Stiles' legs around his waist, slicks his cock up with some more lube and then points it at Stiles' hole.

He struggles to decide where he wants to look. Should he watch himself entering his son's body, or should he watch Stiles' face so that he isn't caught unprepared when he inevitably wakes up? There is no question that he will. The sedatives won't last much longer, and even with prep, being filled up for the first time is bound to be painful enough to finally rouse Stiles.

In the end, Derek chooses to watch his cock.

He stares down his torso as he begins pushing forward, the fat head gradually being swallowed up. Already Derek can see that the thin skin of Stiles' asshole is stretched nearly to its limit, but he keeps going, not stopping until the widest part of his shaft is inside. Stiles makes more noises as Derek enters him, more whines and quiet groans of pain, but nothing else happens until Derek forces the last few inches inside and he is buried all the way.

Then, Stiles groans one last time, drawing Derek's gaze to his face. His brow scrunches up and his fingers tangle in the sheets, his knuckles going white. "Mmm…what?" he mumbles, his voice hoarse as he cracks open his eyes.

Derek holds himself still and waits for Stiles' bleary eyes to clear and alight on him. The boy appears bewildered at first, but then he looks lower and sees that they are both naked. This seems to wake him up to the fact that his ass is stretched beyond belief and he looks back up at Derek's face, his eyes filled with bewilderment and a bit of fear.

"Daddy, it hurts! W-what's going on?" he asks timorously.

"What does it feel like?" Derek responds.

He leaves Stiles' legs where they are and leans down to cover Stiles' smaller body with his larger one like a blanket, his hands planted either side of Stiles' head. Even though their waists aren't aligned, Derek has enough height over his son for his face to hover right above Stiles', blocking out the rest of the world so that he is all that exists to his son. That's how it should always be.

"I don't…why?"

"You're mine, Stiles," Derek says sternly, his tone brooking no argument. "I heard you and Scott earlier. No one can touch you but me."

"B-but you're my daddy!" Stiles warbles, tears forming in his eyes because his body hasn't properly adjusted to accommodate Derek's size just yet. "You can't. This isn't right…"

"It doesn't matter. This is no one's business but ours."

"I don't think I want this. Please…" Despite his protestations, he doesn't try to get out from beneath Derek, and Derek chooses to interpret this as him not really meaning his words.

"You will. You'll learn," he says. If he were a better man, he would be convinced by Stiles' pleas and tears. But he isn't a better man and he can't let go, not now that he has him. "Do you love me?"

Stiles sniffles. "Of course I do."

"Then that's all that matters. I love you, too, so much that I can't let anyone else have you. Now, tell me who I am."

"W-what?"

"Tell me I'm your daddy."

Stiles still looks so unsure, but he obeys nevertheless, his trust for Derek winning out over his fear. "You're my…you're my daddy."

Derek grins down at him. "Again."

"You're my daddy."

"Yes…that's perfect," Derek says heatedly. He finally gives into his body's desires and begins to separate them where they are joined. The sensation of his long, thick cock leaving him causes Stiles to choke on his breath, his arms coming up off of the bedding to grasp at Derek, seeking something to anchor him. Derek pulls out until the head of his cock is all that remains inside, and then he pushes back inside slow as molasses. Even this gentleness isn't enough to stave off the inevitable pain that has Stiles' tears finally falling with a whimper.

"Shh…I've got you," Derek comforts, kissing away the wetness on his son's cheeks as he continues to move inside of him. "It'll get easier."

Now that he is fucking his beautiful boy—no, now that he is _making love_ to him—he is in no hurry. He feels none of his previous urgency because, after years and years of denying himself, he finally has what he wants—Stiles, all to himself. Forever.

He looks down at Stiles' face and uses that as his guide as he switches up the angle of his thrusts, searching for that special spot that will eclipse the pain and have the boy on board with what is happening in no time. It takes Derek a few tries to get it right, but when he does, Stiles' short nails dig into the muscles of his back and he moans loudly, a sound of pleasure instead of pain. His eyes go wide immediately afterward, almost like he has startled himself with his own reaction.

Derek finds this so cute that he just has to kiss him properly, their mouths clashing together. Stiles is shocked into stillness at first, but then he starts reciprocating. He moves his lips inexpertly against Derek's, which makes it clear to the man that his son doesn't have any experience. This revelation excites him, knowing that he is his son's first in every way, and like a reward for waiting for him he aims for Stiles' prostate as often as he can, providing his new lover with as much pleasure as possible.

After a few minutes of this, Stiles' nails don't dig so deeply into Derek's back, his little hole accustomed to his daddy's cock making itself at home inside of it. "D-daddy!" he moans, ripping his mouth from Derek's. His eyes roll back in his head when the man gives a particularly well-aimed thrust.

"You like that, baby?" Derek pants, a sheen of sweat breaking out across his skin.

" _Yes_. Please! Do it again," Stiles implores, spreading his legs wider. "Feels so good."

With a smug smirk, Derek complies. "I told you it would."

He picks up the speed of his thrusts—just slightly, just enough to make it so Stiles struggles to form words under the onslaught on his prostate. He brings their faces close together again so that he can whisper right in Stiles' ear. "Relax, baby boy. Just lie back and let me take care of you," he instructs. "I'll always take good care of you. Gonna make you feel so good. Pump you full of my come. Put my kid in you, yeah… Make you swell."

Stiles doesn't seem to hear him. He just keeps moaning and crying out, "Daddy!" beneath him, his nails leaving red scratches down the length of Derek's back.

Derek doesn't know how much longer he can last. He hasn't gotten laid in a long time, ever since he'd realised that no one else could do it for him like his son, and so he discovers he doesn't possess the stamina he used to. In spite of already coming once a short while ago, he fast feels a second orgasm approaching.

He speeds up his thrusts to the point where they're brutal, fucking Stiles so hard that the headboard slams into the wall and Stiles wails from a mixture of pleasure and pain. Derek connects their mouths again and swallows these amazing noises. He moans as well when he realises he can taste himself, the remnants of come that he'd let dry on Stiles' face tinging their kiss with a salty bitterness.

He manages to last a few more minutes before he is done in by Stiles convulsing suddenly beneath him. His ass tightens around Derek's cock to the point where it's difficult to move, and then wetness spurts between them, his release slicking their stomachs.

The knowledge that his baby boy has come tips Derek over the edge as well. He ends their kiss, presses his face into Stiles' neck and gives a couple more jerky thrusts before staying buried to the hilt. He spills as deep inside Stiles as he can, doing everything he can to ensure that his son ends up knocked up by the end of the night. If it doesn't happen, they'll just have to do it again and again and again, as many times as it takes.

When he comes down from his high, Derek breathes heavily and picks himself up off of his son, who was being crushed beneath the full weight of him. He pulls out of Stiles and lies down beside him, regaining his breath while staring at cheap glow-in-the-dark stars that are stuck to the ceiling. When his lungs no longer burn, Derek breathes through his nose and realises that the whole room reeks of their coupling, something that he feels insanely glad about. He turns his head to look at Stiles next to him and frowns when he sees the boy's worried expression. He pushes himself up to lean on his elbow, giving himself a better view of Stiles' face.

"What's wrong, baby?" he asks.

"Did you really mean all that stuff you said?" the teenager asks.

"You'll have to be more specific."

"About…about getting me pregnant."

Derek blinks a couple of times. "Oh, that. Yeah, I meant it," he says, reaching out with his other hand to rub over Stiles' flat stomach. "You're gonna look so good carrying my kid."

"But _I'm_ your kid."

Ah. Derek gets the worry now. He coos at his boy and pulls him over so that he is lying atop him, his cheek against the centre of Derek's chest. He strokes his fingers through Stiles' hair and smiles when he feels the teenager's arms hugging him fiercely around his middle.

"You _are_ my kid, baby," Derek soothes, running his other hand down the dip of Stiles' spine, making him shudder. "You'll always be my kid and I'll always love you more than anyone else in this world. You'll always come first with me. This is just gonna make me love you even more."

"You promise?" Stiles whispers, sounding a lot younger than fourteen years old. He nuzzles into Derek's chest hair, apparently perfectly comfortable despite his concerns.

Derek kisses the top of Stiles' head. "I promise."

"But how is this going to work? People are gonna ask questions if I suddenly turn up pregnant and stuff."

"We'll lie. We'll have to keep us a secret for now, obviously, but…maybe in four years, when you're eighteen, we can move somewhere far away where nobody knows us. Then we can live openly as a couple. I haven't figured out the ins and outs yet, but I'll make it work. I'm not giving you up for anything."

Stiles is silent for a long time. Derek suspects he is trying to make sense of the unexpected turn his life has taken, trying to come to terms with Derek being both his daddy and his lover. He understands that it's a lot to process, so he gives Stiles all the time he needs while continuing to run his hands through his hair and up and down his back.

Eventually, Stiles speaks. "Alright. I want this."

Derek's heart soars. "I told you that you would. We were meant for each other, I know it."

"Still kinda creepy, though," Stiles points out, picking up his head to look at him. He rests his chin on Derek's chest instead.

"I don't care," the man says vehemently. "You're mine."

"Yeah, yeah, yeah…" Stiles scoffs amusedly, but then he looks up at Derek with his eyes filled with vulnerability. "And you're mine, too, right?"

"Of course," Derek confirms. "I'm your daddy, remember?" His cock twitches valiantly between them, but he doesn't get hard again.

Still, Stiles doesn't miss the twitch. He raises an eyebrow at Derek. "You're really kinky, aren't you?"

"Oh, you'll experience all of my kinks firsthand very soon."

After shaking his head exasperatedly, Stiles lowers it again so that his cheek is once more against Derek's chest. "Whatever. Now shh, I'm sleepy," he mumbles, his eyelids drooping. "Love you, daddy…"

"I love you, too, baby. We can talk more in the morning," Derek accepts, settling in to go to sleep himself.

They _do_ have a lot more to figure out—the acting skills that will be required from both of them to make sure no one else figures out the new part of their relationship; the invasive questions that are sure to come about Stiles' potential pregnancy; the legal things that will have to be sorted if they follow Derek's plan and move away so they can live freely as a couple when Stiles is eighteen. It's all daunting, but just before Derek drifts off, he makes a promise to himself:

Stiles is his now, and he will do everything in his power to make sure he stays that way.

**Author's Note:**

> This is probably the most wrong thing I have ever written...and yet I enjoyed every moment of it, even as I was questioning my own sanity. Once again this turned out longer than I anticipated it would, but I got carried away with Derek admiring Stiles' body and didn't want to trim it down. After all, Stiles' body deserves some admiration, no? Maybe not when he is fourteen, and I'd like to reiterate here that I don't condone this type of thing in real life. But as all of this was fictional, I got down with my bad self, and so did Derek. >:) I admit I kind of fluffed the details at the end, but the smut was the important part anyway, right? :P
> 
> A big thank you to [clavius](http://archiveofourown.org/users/clavius/pseuds/clavius) for this prompt. I hope it was everything you wanted. If anyone else has suggestions for other PWPs they would like to see me tackle, feel free to leave them in a comment down below and, as long as they don't feature something I don't like, I'll try to make them happen. _All_ suggestions are welcome, as long as they're Sterek M/M. I'm really in the mood to write smut right now, so get it while the getting's good! ;)
> 
> **P.S. Don't forget to subscribe to me to be notified when my future fics go live, which will all be Sterek. I've got some good stuff planned. And feel free to check out my past fics if you haven't already. They're good, too.**


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